Kinetic energy is the energy of a moving object, calculated as KE = ½mv². Because speed is squared, small speed increases greatly raise the severity of struck-by injuries.
Kinetic energy is the energy an object has because it is moving. Any moving mass, whether a falling tool, a swinging crane load, a rotating shaft, a flying fragment or a vehicle, carries kinetic energy. When that object strikes a person or another object, the energy is transferred, and the amount transferred largely determines how much damage is done.
In workplace safety, kinetic energy is one of the most common sources of serious injuries and fatalities. Struck-by incidents, caught-in hazards, vehicle collisions and dropped objects all involve moving masses releasing their energy into the human body. Understanding how kinetic energy works helps workers and supervisors judge how severe a hazard really is.
Kinetic energy is closely linked to other forms of energy. An object held at height has potential energy from gravity, which turns into kinetic energy as it falls. A compressed spring or pressurized hose stores energy that can suddenly become motion. Recognizing these energy sources is a core part of hazard identification.
Kinetic energy is calculated with the formula KE = ½mv², where m is the mass of the object and v is its velocity. In metric units, mass is measured in kilograms, velocity in meters per second and energy in joules.
This is why speed limits for forklifts and site vehicles, and controls on work at height, have such a large effect on injury severity. Small reductions in speed produce large reductions in energy.
Many organizations now use energy-based hazard recognition, which teaches workers to look for sources of energy rather than memorizing lists of hazards. Tools such as the energy wheel prompt teams to scan a task for categories of energy, including gravity, motion, mechanical, electrical, pressure, temperature and chemical. Kinetic energy shows up mainly under gravity, motion and mechanical energy.
Research from the Construction Safety Research Alliance and others suggests that once the energy involved in contact with a person exceeds roughly 1,500 joules, a serious injury or fatality becomes a likely outcome. This idea helps teams focus their strongest controls on high-energy tasks.
Controls should follow the hierarchy of controls, with the most reliable controls used for the highest-energy tasks.
At a construction site, workers were installing steel decking three stories above a busy laydown area. During a pre-task review using an energy wheel, the crew noted that a dropped bundle of fasteners or a hand tool could fall more than 10 meters onto people below. The foreman estimated that a falling 2 kg drill would strike with roughly 200 joules of energy, enough to cause a serious injury to anyone below.
The crew set up a barricaded exclusion zone below the work area, required tool lanyards for all hand tools at height and installed toe boards and debris netting along the open edge. Later that week, a worker lost grip on a drill, which was caught by its lanyard before it fell. The site added the energy-based review to its standard pre-task planning for all overhead work.
Kinetic energy equals one-half the mass multiplied by the velocity squared, written as KE = ½mv². With mass in kilograms and velocity in meters per second, the result is in joules.
Because velocity is squared in the formula. Doubling the speed multiplies the energy by two squared, which is four. This is why even small increases in vehicle speed greatly increase the severity of collisions.
A struck-by hazard exists when a moving object can hit a worker. The kinetic energy of that object determines how much force is delivered on impact and how severe the injury is likely to be.
Kinetic energy is the energy of motion. Potential energy is stored energy, such as an object held at height or a compressed spring. Potential energy turns into kinetic energy when the object falls or the spring is released.
Part of SafetyIQ's EHS glossary: plain-English definitions of workplace health and safety terms.
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